An example of a tire air-pressure sensor in the prior art will be briefly described with reference to FIGS. 10 through 12. FIG. 10 is an external appearance perspective view in the case where the prior-art tire air-pressure sensor is arranged and fixed in a wheel. FIG. 11 is a sectional partial view in a radial direction, in the case where a tire is attached to a structure in FIG. 10. FIG. 12 is an enlarged view of that part of an air-pressure sensor element which corresponds to a section A-A in FIG. 10.
Referring to FIGS. 10 through 12, the tire air-pressure sensor 12 is arranged and fixed in a wheel 10 by a band 14. The tire air-pressure sensor 12 is arranged so that its crest side may lie on the outer side of the wheel 10 in the radial direction thereof, and one air vent hole 16 is formed in the crest portion of the case 26 of the tire air-pressure sensor. The air-pressure sensor element 18 is arranged within the case 26, the air vent hole 16 is formed so as to communicate with the sensor portion 18a of the air-pressure sensor element, and an air pressure in the tire 20 acts on the sensor portion 18a of the air-pressure sensor element 18 through the air vent hole 16, thereby to be detected. Incidentally, a circuit board 22 is disposed in the case 26, the air-pressure sensor element 18 is mounted on the circuit board 22, while a transmitter and a battery, not shown, are mounted thereon, and the interior of the case 26 is molded with a resin 24 for the purpose of waterproofness, whereby the tire air-pressure sensor 12 is configured. A signal which corresponds to the air pressure detected by the air-pressure sensor element 18 is appropriately transmitted to a receiver in a vehicle, and the air pressure in the tire 20 is monitored.
Those structures of the tire air-pressure sensor 12 in which, likewise to such a prior-art structure, the air pressure in the tire 20 is exerted on the sensor portion 18a of the air-pressure sensor 18 through the air vent hole 16 of simple shape, are disclosed in JP-A-2002-1440, JP-A-2005-47466, etc.